JP4988399B2 - Pre-control method of lambda value - Google Patents

Description

  The present invention relates to a method for pre-control (open loop control) of a lambda value during a heating phase (superheated phase) of an exhaust gas purification facility of an internal combustion engine comprising at least one catalytic device and at least one lambda sensor. About.

  In order to meet stringent exhaust gas standards in heat engines, the catalyst must be heated to the proper operating temperature as quickly as possible at the start, along with the minimization of raw exhaust gas. For that purpose, various measures such as raising the exhaust gas temperature by delayed ignition, over-concentration of the air-fuel mixture combined with secondary air blowing, and the use of a glow plug in the exhaust gas path in front of the catalytic device, etc. It has been known. In the case of an engine equipped with an exhaust gas turbocharger and a supercharging pressure control valve, the supercharging pressure control valve can be opened for rapid heating of the catalyst device. All of these measures are on the one hand on exhaust gas concepts such as rich or lean, and on the other hand available hardware (eg supercharged valve, secondary air blowing device, camshaft adjustment, etc.) Depends on and affects the exhaust gas chamber. Based on the provisions of the law, their effects must be checked in cars with on-board diagnostic functions. If any of these measures do not work well during a cold start, the exhaust gas limits may not be met.

  On the other hand, regarding the conversion of harmful gas components, there is a particular interest in the storage capacity OSC (Oxygen Storage Capacity) of the catalytic device for oxygen. The storage capacity of the exhaust gas purification equipment for oxygen is used to take up oxygen in the lean stage and release it again in the rich stage. Thereby, the harmful gas component to be oxidized of the exhaust gas can be converted. As the exhaust gas purification equipment ages, the storage capacity of the equipment for oxygen decreases. As a result, sufficient oxygen is no longer available to purify the exhaust gas from harmful gas components in the over-rich stage, and the lambda sensor behind the exhaust gas purification equipment detects those components to be oxidized. The lambda sensor further detects oxygen in a longer lean phase, which oxygen can no longer be stored by the exhaust gas purification equipment. In many countries, the law mandates that the exhaust gas purification equipment be checked by the engine controller during driving (onboard diagnostics). In doing so, the diagnosis of the active (active) catalytic device is aimed at detecting and displaying through the control lamp an unacceptable reduction in conversion which results in an unacceptable increase in the exhaust gas value.

The catalyst diagnosis for measuring oxygen is performed as follows using a wideband sensor.
The catalyst is first deoxygenated by a rich mixture (λ <1). After this stage, which is called condition adjustment, lean exhaust gas (λ> 1) is fed, and the amount of oxygen fed at that time is integrated. During this measurement phase, if the sensor behind the catalytic device indicates a lean or oxygen-containing mixture, the integrated quantity is the actual oxygen of the catalyst, which is a measure for quality. Corresponds to storage capacity. This method is applied over and over again.

  DE 41 12 478 C2 describes a method for determining the aging state of a catalyst, in which the lambda value is measured in front and behind the catalytic device. During control oscillations from rich to lean or in the opposite direction before the catalyst, the lambda value behind the catalyst shows a corresponding shift and the mass flow rate of the gas flowing through the catalyst is determined The time integral of the product of the gas mass flow rate and the lambda value before the catalytic device is calculated, the time integral of the product of the gas mass flow rate and the lambda value behind the catalytic device is calculated, and the aging state of the catalyst As a measure for the above, the difference between the two integral values or the quotient obtained from the two integral values or the quotient obtained from one of the difference and the two integral values is used. The disadvantage of the method described there is that an exhaust gas purification facility is used to determine the amount of oxygen fed or removed through the integration of the product obtained from the actual lambda value and the gas mass flow rate. It is necessary to measure the lambda value before this value using an expensive wideband lambda sensor.

  Another method for determining the oxygen storage capacity of exhaust gas purification equipment is described in EP 0546 318 B1. This system initially gives a lambda change in which the oxygen deficient input is higher than the oxygen storage capacity of the catalyst. This oxygen input is chosen so that the catalysts are each filled to the limit of their capacity in the lean stage. To determine the oxygen storage capacity of the catalyst, the average lambda value before the catalytic device is intentionally moved in the lean direction during the lambda oscillation of the system, thereby reducing the oxygen removal from stage to stage. . Oxygen storage capacity can be determined by determining the number of over- / deep-lean transitions displayed by the lambda sensor located behind the catalytic device, which means that the increased number of steps reduces the storage capacity. ing. The disadvantage with this method is that exhaust gas that has not been purified is delivered to the lean stage.

  DE 102409777 A1 describes a method for operating an internal combustion engine with a direct fuel injection system, in particular for motor vehicles, in which an exhaust gas system with at least one catalytic device is provided. In order to heat at least one of these catalytic devices, the internal combustion engine is operated with λ> 1 to fill the oxygen storage device of at least one catalytic device during cyclic lean operation, and also over-rich operation Some are operated at λ <1 in order to heat the catalyst by the reaction heat of the reaction between oxygen and unburned fuel components in at least one catalytic device. In that case, first, the oxygen storage capacity of each individual catalyst device or a group of catalyst devices is determined by lambda jump, and the calorific value related to oxygen is determined through the current oxygen storage capacity of one or more catalysts obtained. The energy supply is determined, taking into account the exhaust gas lambda and the exhaust gas mass flow, and thereby the temperature in at least one catalytic device. Thereby, the heating control of one or a plurality of catalyst devices is performed through adjustment of the rich stage and / or the lean stage.

  Due to the prior art, a slightly lean mixture after start is controlled with λ> 1 for rapid heating of the catalytic device. Particularly during a cold start, since the dew point has not yet been reached for the lambda sensor, the operational ready state of the lambda sensor is clearly reached only after the start. Therefore, the lambda value is pre-controlled immediately after the start with λ> 1 and in this case is generally around 1.05. This ensures that a slightly lean lambda is always maintained, even if there are variations in fuel metering due to mass production. The interruption of the lambda value λ = 1 leads in part to a significant increase in CO emissions and HC emissions, and in some circumstances may exceed the corresponding emission limits. However, after exceeding the so-called “light-off temperature” (the temperature at which the catalyst reaches the optimum reaction temperature and thus allows the catalyst to act in principle as a three-way catalyst) by dilute lambda. However, nitrogen oxides in the exhaust gas cannot be converted.

  The object of the present invention is to provide a method that guarantees at least partial conversion of NOx already during the heating stage of the catalytic device and does not violate the limit values for the components to be oxidized during this stage. is there.

  The above object is to provide a method for pre-controlling lambda values during a heating phase of an exhaust gas purification equipment of an internal combustion engine having at least one catalyst device and at least one lambda (λ) sensor. A lambda change is preset at least temporarily during the heating phase of the catalytic device, using a higher frequency modulation, during which a temporal lambda average of λ> 1 is preset and at least temporarily This is solved by being controlled so that a lambda value of λ <1 is achieved.

  According to the invention, this intentional control strategy for lambda already achieves a lambda value of λ <1 at least temporarily during this stage, so that a partial conversion of nitrogen oxides is achieved. At the same time, the average sparse lambda value does not negatively affect the conversion of components to be oxidized, such as HC and CO. It was even observed that this pre-control strategy also supported the conversion of the components to be oxidized to a small extent. In that case, since the variation due to mass production is reliably covered by the prior control to λ> 1, for example, λ = 1.05, there is a risk of exceeding the limit value relating to the component to be oxidized already explained above. No.

  In that case, the addition of the higher frequency modulation is pre-controlled between the λ> 1 and λ <1 stages, according to a preferred manner, with a lambda change of lambda pre-control with an asymmetric on / off ratio, In some cases, the lambda value is controlled from a value clearly less than 1 in a relatively short time, so that the lambda is relatively long to ensure the conversion of components to be oxidized, such as HC and CO. It can remain at time λ> 1. In contrast, a lambda value clearly less than 1 accelerates the conversion of nitrogen oxides.

  Furthermore, it is conceivable that the higher frequency modulation is varied depending on the operating point of the internal combustion engine with respect to amplitude and / or frequency, whereby a flexible lambda pre-control can be achieved.

  For example, since the oxygen storage capacity (OSC) of one or more catalytic devices undergoes a certain amount of aging, according to the present invention, a higher frequency modulation frequency may be used for the oxygen storage capacity (OSC) of one or more catalytic devices. Can be considered to fit the actual value of). Thus, this lambda pre-control guarantees as constant a conversion rate as possible of nitrogen oxides on the one hand and HC or CO on the other hand, which in particular relates to these harmful substance components even after some aging. The retention of the limit value is guaranteed.

  In general, it is advantageous and advantageous if a higher frequency modulation frequency is increased as the oxygen storage capacity (OSC) value of one or more catalytic devices decreases. This can reduce the risk of appearance of over-rich peaks.

  In this case, this method contemplates measuring and storing the actual value of the oxygen storage capacity (OSC) of one or more catalytic devices by a diagnostic method relating to the oxygen storage capacity (OSC). This value can then be used directly for frequency, amplitude, and in some cases, calculation of the optimum modulation for the on / off ratio between the λ> 1 and λ <1 steps.

  In addition to the oxygen storage capacity (OSC) of one or more catalytic devices, volume weighting of the catalyst temperature is performed, and this is one of the amplitude modulation and / or frequency modulation of the lambda change over time of the lambda pre-control. Alternatively, when considered during heating of the plurality of catalytic devices, the actual oxygen storage capacity as a function of temperature in the one or more catalytic devices can be determined therefrom. Since the catalytic device is heated from the front side to the rear side (as viewed in the gas flow direction) during the heating process, this volume weighting can define a characteristic catalyst temperature for all catalytic devices. This catalyst temperature is then used for subsequent calculations.

  In this case, in a particularly advantageous variant of the method, the value of the oxygen storage capacity (OSC) of one or more catalytic devices and the value for volume weighting of the catalyst temperature are measured and stored in a characteristic map. Is considered. Thereby, complex functional relationships are also advantageously expressed and evaluated.

  In the method described above, it can be considered to limit the amplitude of the modulation of the lambda pre-control temporal lambda change. This is particularly significant with respect to running stability, especially when sparse lambda values are pre-controlled.

  If the measures described above are applied during catalyst heating and before reaching the ready state of operation of the lambda sensor, the action of the one or more catalyst devices can be further enhanced somewhat. The measure is advantageous even before reaching the light-off stage, in which the increase in the activity of one or more catalytic devices for the conversion of the components to be oxidized (HC, CO) is the usual λ It can be seen by the lambda modulation from the driving of = 1.

  If this measure is applied to a gasoline direct injection or intake manifold internal combustion engine, this control strategy is combined with a known "homogeneous split" mode of operation, especially for gasoline direct injection internal combustion engines. . This is because here lean operation is improved compared to pure homogeneous operation. In principle, driving mode changes could be combined with it. So, for example, if the combustion method allows it, a stratified mode of operation is selected in the lean portion of the amplitude, and a homogeneous mode of operation is operated in the rich portion of the amplitude. This strategy can also be applied here if lean drivability is obtained in the required region for the intake manifold injection type.

The invention is explained in more detail below on the basis of the embodiment shown in the drawing.
The technical environment to which the method according to the present invention is applied assumes, for example, an internal combustion engine comprising an engine block and an air intake canal for supplying combustion air to the engine block. There, the amount of air in the air intake canal can be determined using an intake air measuring device. The exhaust gas of the internal combustion engine is sent through an exhaust gas purification facility having an exhaust gas canal as a main component, and in this exhaust gas canal, a first lambda sensor is disposed in front of the catalyst device when viewed in the direction of the exhaust gas flow, A second lambda sensor is disposed behind the catalytic device. The exhaust gas purification equipment can further include a second catalytic device behind the second lambda sensor. These lambda sensors are connected to a control device, which calculates the mixture from the lambda sensor data and the intake air measurement device data and measures the fuel by the corresponding injection nozzle in the air intake canal. Control the fuel metering device for distribution.

  A lambda sensor located in the exhaust gas canal behind the engine block adjusts the lambda value suitable for achieving the optimum purification effect for the exhaust gas purification equipment by the control device. The lambda sensor can be made as a simple jump sensor or as an expensive wideband sensor, which determines the excess air ratio λ over a wide range. If the lambda sensor is made as a jump sensor, it is advantageous in terms of cost, but it can only be adjusted to a reference value of λ = 1. Therefore, none of the lambda control devices works while determining the oxygen storage capacity. In this operation phase, only pre-control of the fuel mixture using the lambda value determined in advance by the control device is performed. A second lambda sensor located behind the first catalytic device in the exhaust gas canal is also evaluated in the control device and used to determine the oxygen storage capacity of the exhaust gas purification equipment in a manner based on the prior art. Can be done.

  The control device is further connected to a display / storage unit, which can, for example, indicate a fault in the exhaust gas purification facility. Furthermore, if this unit requires the oxygen storage capacity of the catalytic device, for example during on-board diagnostics, how much storage capacity has already been set as a limit value in order to comply with legal exhaust gas regulations. Can also be displayed.

  In order to determine the oxygen storage capacity, in general during onboard diagnostics, the internal combustion engine will first have a long enough fuel excess (“rich mixture”) to reduce all the oxygen in the catalytic device. It is driven in the state. During the subsequent lean operation, oxygen is taken into the catalyst device and at that time it is determined by the lambda sensor behind the catalyst device when the exhaust gas rich in oxygen has appeared. This is because the oxygen storage capacity OSC is exceeded at that time.

  The prior art sets a jump alternation between λ <1 and λ> 1. During this pre-control, there may be errors caused by, for example, injection valve variations or errors in air supply measurement. Such an error will cause the lambda value to be distorted and thereby cause an error in determining the oxygen storage capacity.

  During the heating phase immediately after the start of the internal combustion engine, it is considered that a somewhat lean mixture with λ> 1 is fed after the start in order to heat the catalyst device quickly. Particularly during a cold start, the dew point of the lambda sensor has not yet been interrupted, so that the lambda sensor ready for operation is clearly reached only after the start.

  As schematically shown in FIGS. 1 a and 1 b, the lambda (λ) pre-control 10 temporal lambda (λ) during the heating phase of the catalytic device during the heating phase of the exhaust gas purification equipment of the internal combustion engine. The change 11 is pre-established with a temporal lambda (λ) average value of λ> 1 in this stage, at least temporarily using higher frequency modulation, and in the example shown, λ = 1.05. It is set and controlled so that a lambda value of λ <1 is reached at least temporarily. FIG. 1 a shows a variant of this method with a symmetrical lambda pre-control 10. FIG. 1b shows a variant of this method in which the temporal lambda change 11 of the lambda pre-control 10 is pre-controlled with an asymmetric on / off ratio between the λ> 1 and λ <1 steps. Yes.

  The region 20 of NOx conversion is in the region of the temporal lambda change 11 with λ <1 as long as the light-off phase of one or more catalytic devices, ie the reaction temperature, has been reached. NOx reduced in the overconcentration stage is not formed again for reasons of reaction motion in the catalyst or further in the exhaust gas path thereafter. However, in this regard, NOx conversion rates of> 99% efficiency as achieved during controlled λ = 1 operation of the three-way catalyst cannot be achieved by the method of the present invention. It should be pointed out that achieving such a NOx = conversion rate of> 99% is not the goal of the strategy described here.

  According to the invention, it is envisaged that the higher frequency modulation with respect to the amplitude 13 and / or the frequency is varied depending on the operating point of the internal combustion engine. According to this method, a higher frequency modulation amplitude 13 can be adapted to the actual value of the oxygen storage capacity (OSC) of one or more catalytic devices. Furthermore, the frequency of higher frequency modulation can be increased as the oxygen storage capacity (OSC) value of one or more catalytic devices decreases.

  The actual value of the oxygen storage capacity (OSC) of one or more catalytic devices can be measured and stored by a diagnostic method relating to the oxygen storage capacity (OSC), as already described above. In addition to the oxygen storage capacity (OSC) of one or more catalyst devices, volume weighting of the catalyst temperature is performed, which is the temporal lambda change 11 of the lambda pre-control 10 during heating of the one or more catalyst devices. Can be taken into account during amplitude modulation and / or frequency modulation. In a preferred variant of this method for the calculation of the modulation amplitude 13 and the frequency, the oxygen storage capacity (OSC) value of one or more catalytic devices and the value for volume weighting of the catalyst temperature are measured and characterized. Stored in the map.

  The strategy described above is used below in various stages of heating of the catalytic device as shown by the table below, and the above measures are taken during heating of the catalytic device and preparation of the lambda sensor for operation. Applied before completion is reached.

  Application before stage B, i.e., reaching the reaction start temperature ("light off" temperature) of the catalyst, is one or more for the conversion of the components to be oxidized (HC, CO) in addition to the improvement of NOx conversion. This can be meaningful as long as an increase in the activity of the catalytic device is observed. Further, depending on the system design or application, stage D may be omitted, in which case it can be shifted directly to normal operation without further catalyst heating measures. In this case, this can be done in a phase with a controlled or uncontrolled lambda, depending on whether the lambda sensor is ready for operation. It is also possible to transfer this open loop control strategy to a closed loop control strategy during stage D when the lambda sensor is ready for operation. The preset value for lambda is introduced as a preset reference value directly into the lambda adjustment (lambda closed loop control).

FIG. 2 schematically shows the temporal change of the temporal lambda change 11, the oxygen concentration 40 and the concentrations 30 and 60 of various harmful substances.
Depending on the frequency and amplitude 13 adjustment, in the example shown, a NOx conversion of more than 50% is achieved compared to pre-controlled operation with a constant lambda value of λ = 1.04. At this time, it is recognized that the NOx concentration 30 gradually decreases as the modulation amplitude 13 for lambda pre-control increases. FIG. 2 also shows that when the amplitude 13 is small and the lambda value is not pre-controlled to less than 1, no reduction in the NOx concentration 30 is observed at all. Only when the amplitude 13 increases, the NOx concentration 30 decreases. At that time, the oxygen concentration 40 is constantly kept at approximately 0.6% over a wide range. The over-concentration peak from the over-concentration lambda pre-controlled by the oxygen storage capacity (OSC) always present in the three-way catalyst is well captured, so if the frequency and amplitude 13 are set appropriately The appearance of CO and HC as a problem is not expected, as the temporal changes for CO concentration 50 and HC concentration 60 indicate.

  According to this method, the lambda pre-open (open loop) control is realized immediately after the start of the internal combustion engine and before the lambda (closed loop) control is ready for operation, and this control is performed during the heating stage of the catalyst device. Already partial conversion of the nitrogen oxide has already been carried out, which does not lead to any problematic deterioration of the components to be oxidized. Another advantage of this strategy is, for example, that it is necessary for operating at λ = 1, so that a precise lambda value is required, so that a lambda sensor ready for control (closed loop) is required. There is no indication.

It is the schematic of symmetrical lambda pre-control. It is the schematic of asymmetrical lambda pre-control. It is the schematic of the lambda value, oxygen concentration, and the time change of the density | concentration of various harmful | toxic substances.

Explanation of symbols

10 ... Lambda pre-control 11 ... Time lambda change 12 ... Time lambda average 13 ... Amplitude 20 ... NOx conversion region λ ... Air excess ratio 30 ... NOx concentration 40 ... Oxygen concentration 50 ... CO concentration 60 ... toxic substance concentration

Claims (9)

In a method for pre-controlling a lambda value during a heating phase of an exhaust gas purification equipment of an internal combustion engine comprising at least one catalytic device and at least one lambda (λ) sensor,
The lambda change (11) in time of the lambda pre-control (10) is used at least temporarily during this phase of heating to the operating temperature of the catalytic device, during this phase using λ> A temporal lambda average value of 12 (12) is preset and controlled to at least temporarily achieve a lambda value of λ <1;
The pre-control of the lambda value is applied during the heating phase of the catalytic device and before the lambda sensor reaches the ready state of operation;
A lambda value pre-control method characterized by:   The lambda pre-control (10) temporal lambda change (11) is pre-controlled between λ> 1 and λ <1 stages with an asymmetric on / off ratio. Advance control method. Pre control method according to claim 1 wherein the higher frequency modulation amplitude (13), characterized in that it is adapted to the actual value of the oxygen storage capacity of the one or more catalytic converter (OSC). Pre control method according to claim 1, wherein the frequency of the high frequency modulation than is the value of the oxygen storage capacity (OSC) of one or more catalytic device, characterized in that the increased along with the decrease. The actual value of the oxygen storage capability (OSC) of the one or more catalytic device, according to claim 3 or 4, characterized in that it is sought and stored using a diagnostic method for the oxygen storage capacity (OSC) Prior control method. In addition to the oxygen storage capacity (OSC) of the one or more catalytic devices, a volume weighting of the temperature of the catalytic device is performed, and this weighting is applied to the lambda during the heating phase of the one or more catalytic devices. amplitude modulation and advance control method according to any one of claims 3 to 5, characterized in that it is considered in at least one of the frequency modulation of the temporal lambda variation of precontrol (10) (11). And values for the oxygen storage capacity (OSC) of the one or more catalyst apparatuses, the measured and the values for the volume weighted temperature of the catalytic converter, be and registered in the characteristic map to claim 6, wherein The pre-control method described. Pre control method according to any one of claims 1 to 7, characterized in that lambda pre amplitude of the modulation of the temporal lambda change in the control (10) (11) (13) is limited. Pre control method according to any one of claims 1 to 8, characterized in that it is applied to a gasoline direct injection type or manifold injection type internal combustion engine.

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